Mercury lamps, sodium lamps, metal-halide lamps and ceramic metal-halide lamps are known as high-intensity discharge lamps. Metal-halide lamps use metal halides as luminous materials and therefore are not only high in lamp efficacy (or luminous efficacy) but also excellent in color characteristics such as correlated color temperature, chromaticity deviation and color rendering property. While metal-halide lamps include discharge tubes made of quartz glass, ceramic metal-halide lamps include discharge tubes made of translucent ceramics. Therefore ceramic metal-halide lamps are not only excellent in lamp efficacy and color characteristics but also long in lamp life and high in stability.
In general, it is said that ceramic metal-halide lamps suffer from an incompatible relation between lamp efficacy and color characteristics and it is difficult to obtain both high lamp efficacy and excellent color characteristics in ceramic metal-halide lamps. That is, improvement of lamp efficacy tends to deteriorate color characteristics and improvement of color characteristics tends to deteriorate lamp efficacy.